Space spanning structures such as bridges, docks, piers, load bearing walls, hulls, and decks which have provided a span across bodies of water, separations of land and water and/or open voids have long been made of materials such as concrete, steel or wood. Concrete has been used in building bridges and other structures including the columns, decks, and beams which support these structures.
Such concrete structures are typically constructed with the concrete poured in situ as well as using some preformed components precast into structural components such as supports and transported to the site of the construction.
Constructing such concrete structures in situ requires hauling building materials and heavy equipment and pouring and casting the components on site. This process of construction involves a long construction time and is generally costly, subject to delay due to weather and environmental conditions, and disruptive to existing traffic patterns when constructing a bridge on an existing roadway.
On the other hand, pre-cast concrete structural components are extremely heavy and bulky and are typically costly and difficult to transport to the site of construction due in part to their bulkiness and heavy weight. Although construction time is shortened as compared to poured in situ, extensive time with resulting delays is still a factor. Bridge construction with such precast forms is particularly difficult, if not impossible, in remote or difficult terrain such as mountains or jungle areas in which numerous bridges are constructed.
In addition to construction and shipping difficulties with concrete bridge structures, the low tensile strength of concrete can result in failures in concrete bridge structures, particularly in the surface of bridge components. Reinforcement is often required in such concrete structures when subjected to large loads such as in highway bridges. Steel and other materials have been used to reinforce concrete structures. If not properly installed, such reinforcements cause cracking and failure in the reinforced concrete, thereby weakening the entire structure. Further, the inherent hollow spaces which exist in concrete are highly subject to environmental degradation. Also, poor workmanship often contributes to the rate of deterioration.
In addition to concrete, steel also has been widely used by itself as a building material for structural components in structures such as bridges, barge decks, vessel hulls, and load bearing walls. While having certain desirable strength properties, steel is quite heavy and costly to ship and can share construction difficulties with concrete as described.
Steel and concrete are also susceptible to corrosive elements, such as water, salt water and agents present in the environment such as acid rain, road salts, chemicals, oxygen and the like. Environmental exposure of concrete structures leads to pitting and spalling in concrete and thereby results in severe cracking and a significant decrease in strength in the concrete structure. Steel is likewise susceptible to corrosion, such as rust, by chemical attack. The rusting of steel weakens the steel, transferring tensile load to the concrete, thereby cracking the structure. The rusting of steel in stand alone applications requires ongoing maintenance, and after a period of time corrosion can result in failure of the structure. The planned life of steel structures is likewise reduced by rust.
The susceptibility to environmental attack of steel requires costly and frequent maintenance and preventative measures such as painting and surface treatments. In completed structures, such painting and surface treatment is often dangerous and time consuming, as workers are forced to treat the steel components in situ while exposed to dangerous conditions such as road traffic, wind, rain, lightning, sun and the like. The susceptibility of steel to environmental attack also requires the use of costly alloys in certain applications.
Wood has been another long-time building material for bridges and other structures. Wood, like concrete and steel, is also susceptible to environmental attack, especially rot from weather and termites. In such environments, wood encounters a drastic reduction in strength which compromises the integrity of the structure. Moreover, wood undergoes accelerated deterioration in structures in marine environments.
Along with environmental attack, deterioration and damage to bridges and other traffic and weight bearing structures occurs as a result of heavy use. Traffic bearing structures encounter repeated heavy loads of moving vehicles, stresses from wind, earthquakes and the like which cause deterioration of the materials and structure.
For the reasons described above, the United States Department of Transportation "Bridge Inventory" reflects several hundred thousand structures, approximately forty percent of bridges in the United States, made from concrete, steel and wood are poorly maintained and in need of rehabilitation in the United States. The same is believed to be true for other nations.
The associated repairs for such structures are extremely costly and difficult to undertake. Steel, concrete and wood structures need welding, reinforcement and replacement. Decks and hulls of structures in marine environments rust, requiring constant maintenance and vigilance. In numerous instances, such repairs are not feasible or economically justifiable and cannot be undertaken, and thereby require the replacement of the structure. Further, in developing areas where infrastructures are in need of development or improvement, constructing bridges and other such structures utilizing concrete, steel and wood face unique difficulties. Difficulty and high cost has been associated with transporting materials to remote locations to construct bridges with concrete and steel. This process is more costly in marine environments where repairs require costly dry-docking or transport of materials. Also, the degree of labor and skill is very high using traditional building materials and methods.
Further, traditional construction methods have generally taken long time periods and required large equipment and massive labor costs. Thus, development and repair of infrastructures through the world has been hampered or even precluded due to the cost and difficulty of construction. Further, in areas where structures have been damaged due to deterioration or destroyed by natural disaster, such as earthquake, hurricane, or tornado, repair can be disruptive to traffic or use of the bridge or structure or even delayed or prevented due to construction costs.
In addressing the limitations of existing concrete, wood and steel structures, some fiber reinforced polymer composite materials have been explored for use in constructing parts of bridges including foot traffic bridges, piers, and decks and hulls of some small vessels. Fiber reinforced polymers have been investigated for incorporation into foot bridges and some other structural uses such as houses, catwalks, and skyscraper towers. These composite materials have been utilized in conjunction with, and as an alternative to, steel, wood or concrete due to their high strength, light weight and highly corrosion resistant properties. However, it is believed that construction of traffic bridges, marine decking systems, and other load bearing applications built with polymer matrix composite materials have not been widely implemented due to extremely high costs of materials and uncertain performance, including doubts about long term durability and maintenance.
As cost is significant in the bridge construction industry, such materials have not been considered feasible alternatives for many weight bearing traffic bridge designs. For example, high performance composites made with relatively expensive carbon fibers have frequently been eliminated by cost considerations. These same cost considerations have inhibited the use of composite materials in decking and hull applications.
In view of the problems associated with bridges and other structures formed of steel, concrete, and wood described herein, there remains a need for a bridge or like support structure with the following characteristics: light-weight; low cost, pre-manufactured; constructed of structural modular components; easily shipped, constructed, and repaired without requiring extensive heavy machinery; and resistant to corrosion and environmental attack, even without surface treatment. There is also a need for a support structure which can provide the structural strength and stiffness for constructing a highway bridge or similar support structure.